Does hypothyroidism (underactive thyroid) affect blood pressure?

From the Guidelines

Hypothyroidism can affect blood pressure, typically causing mild hypertension, often diastolic, due to increased systemic vascular resistance and decreased cardiac output. This occurs because thyroid hormones play a crucial role in regulating heart rate and blood vessel function. When thyroid hormone levels are low, heart rate slows down, and blood vessels become less elastic, affecting circulation throughout the body 1. Additionally, hypothyroidism can lead to increased cholesterol levels and arterial stiffness, which may contribute to hypertension in some cases.

Key Points to Consider

• Hypothyroidism is associated with bradycardia, mild hypertension, and a narrowed pulse pressure 1
• The low cardiac output in hypothyroidism is caused by bradycardia, a decrease in ventricular filling, and a decrease in cardiac contractility 1
• Systemic vascular resistance can increase by as much as 50%, and diastolic relaxation and filling are slowed in hypothyroidism 1
• Treatment involves thyroid hormone replacement therapy, usually with levothyroxine, to restore normal thyroid hormone levels and improve cardiovascular function 1

Treatment and Management

• Thyroid hormone replacement therapy is recommended to manage hypothyroidism and its effects on blood pressure 1
• Patients should monitor their blood pressure closely, and those who experience an increase in blood pressure should be treated with antihypertensives 1
• Regular monitoring of both thyroid function and blood pressure is important during treatment adjustment periods to ensure optimal management of hypothyroidism and its cardiovascular effects.

From the FDA Drug Label

Administration of sertraline in patients stabilized on levothyroxine sodium may result in increased levothyroxine sodium requirements. Concurrent use of ketamine and levothyroxine sodium may produce marked hypertension and tachycardia. Concurrent use of sympathomimetics and levothyroxine sodium may increase the effects of sympathomimetics or thyroid hormone. Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease. Clinical Considerations Disease-Associated Maternal and/or Embryo/Fetal Risk Maternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre‑eclampsia, stillbirth, and premature delivery. Cardiovascular:palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest

Hypothyroidism and its treatment with levothyroxine may have an indirect effect on blood pressure.

• Untreated hypothyroidism has been associated with a higher risk of gestational hypertension and pre-eclampsia in pregnant women.
• Levothyroxine therapy may increase the risk of coronary insufficiency when used with sympathomimetic agents in patients with coronary artery disease.
• Overdosage of levothyroxine can cause symptoms of hyperthyroidism, including increased pulse and blood pressure. However, there is no direct information in the provided drug labels that hypothyroidism itself affects blood pressure 2, 2.

From the Research

Hypothyroidism and Blood Pressure

• Hypothyroidism has been associated with diastolic hypertension, with studies showing that the induction of hypothyroidism can significantly increase diastolic blood pressure 3.
• The prevalence of hypothyroidism in hypertensive patients has been found to be around 3.6%, with restoration of normal serum thyroxine and thyrotropin levels leading to a decrease in diastolic blood pressure in some patients 3.
• Treatment of hypothyroidism with levothyroxine therapy has been shown to decrease blood pressure in some patients, although the effect can vary depending on the individual 4.

Mechanisms of Hypothyroidism-Related Hypertension

• Increased peripheral vascular resistance and low cardiac output have been suggested as possible links between hypothyroidism and diastolic hypertension 5.
• Aortic stiffness has also been found to be increased in patients with hypothyroidism and hypertension, which can contribute to sustained hypertension 4.
• The hypothyroid population is characterized by significant volume changes, initiating a volume-dependent, low plasma renin activity mechanism of blood pressure elevation 5.

Effects of Thyroid Hormone on Blood Pressure Regulation

• Thyroid hormone has well-recognized effects on the cardiovascular system and blood pressure regulation, with hypothyroidism leading to decreased cardiac output, narrow pulse pressure, increased systemic vascular resistance, and decreased metabolic rate 6.
• The effects of thyroid hormone on blood pressure are complex and involve adaptations of the cardiovascular system to accommodate changes in demand 6.
• Variations from the euthyroid status can affect virtually all physiological systems, but the effects on the cardiovascular system are particularly pronounced 7.

Clinical Implications

• Hypothyroidism is a cause of secondary hypertension, and treatment of hypothyroidism can lead to normalization of blood pressure in some patients 5.
• The regulation of blood pressure and the development and maintenance of variable forms of arterial hypertension are different in thyroid disorders, with hypothyroidism typically resulting in a low-renin form of hypertension 7.
• Antihypertensive treatment in thyroid disorders may require different approaches, with calcium-channel blockers and diuretics potentially being more effective in hypothyroidism 7.